Actuator

ABSTRACT

The actuator is used in a pickup device for a drive device of an optical disc. The actuator is positioned opposing to the optical disc to irradiates a light beam from a light source to an information recording surface of the optical disc. The objective lens is fixed at on the lens holder forming the actuator at a position closer to one end thereof. One coil substrate is fixed on one side face of the lens holder in a range from the one end of the lens holder to a center portion of the lens holder, and the other coil substrate is fixed on the other side face of the lens holder in a range from the other end of the lens holder to the center portion of the lens holder. Therefore, near the end of the lens holder on the objective lens side, the coil substrate is not attached to one side of the lens holder, providing a space below the objective lens. By arranging an optical system to guide the light beam to the objective lens via the space, the optical system can be arranged at the same height level as the actuator.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a pickup device of a disc drivefor optically writing and reading information on an optical disc and,more particularly, to a pickup device suitable for a thin disc drive.

[0003] 2. Description of Related Art

[0004] A disc drive for recording information on and reproducinginformation from an optical disc such as a CD (Compact Disc) and a DVD(Digital Video Disc) includes an optical pickup device. In order toaccurately record and reproduce information on and from an optical disc,the pickup device performs a focus control for controlling a distancebetween an objective lens and an information recording surface of theoptical disc and performs a tracking control for controlling theobjective lens to follow an information track of the optical disc.

[0005] The pickup device directs a laser beam, which is emitted from alight source such as a laser diode, to the objective lens by usingpredetermined optical system components, and irradiates the laser beamonto the information recording surface of the optical disc via theobjective lens. Normally, the objective lens is positioned to oppose tothe optical disc. A laser beam from the light source is guided by theoptical system components to a position below the objective lens alongan optical path provided in parallel with the optical disc. Then, thelaser beam is changed its path by a raise-up mirror placed under theobjective lens to a vertical direction, that is, the direction of theobjective lens, and the laser beam reaches the objective lens. Theobjective lens is mounted on a lens holder and coil substrates aremounted on the lens holder. The lens holder is moved vertically andhorizontally with respect to the optical disc by applying drivingcurrent to the coil substrates in a magnetic field formed by the magnetswhich are placed close to each other, so that the focus control and thetracking control are performed. An example of such a pickup device isdescribed in Japanese Patent Laid-Open under No. 2001-229557.

[0006] However, in the above-described pickup device, since the coilsubstrates are mounted on the opposing sides of the rectangular lensholder, the optical path of a laser beam from the laser light sourcecannot be arranged at the same height level as the coil substrates inthe horizontal direction. Namely, since the paired coil substrates arepositioned on both sides of the objective lens, the coil substratesbecome obstacles and prevent a laser beam from being guided to theposition below the objective lens at the same height level as the coilsubstrates. For this reason, in the pickup device described in JapanesePatent Laid-Open under No. 2001-229557, for example, the optical path ofa laser beam is placed below the lens holder. Namely, the optical pathis arranged such that the laser beam is directed to the position belowthe objective lens at a lower level than the coil substrates and thendirected to the objective lens by the raise-up mirror.

[0007] However, when the optical path of a laser beam is placed at alower height level than the lens holder, the whole height (thickness inthe vertical direction) of the pickup increases. For example, in a thindrive device such as a drive device mounted in a notebook-type personalcomputer, a thin pickup device has to be used and thus the above thickpickup device cannot be used.

SUMMARY OF THE INVENTION

[0008] The present invention is devised in view of the above-describedpoint, and its object is to provide an actuator for a thin pickup devicewhich is suitable for use in a thin drive device.

[0009] According to one aspect of the present invention, there isprovided an actuator including: a lens holder having an upper face forholding an objective lens and a pair of side faces for holding coilsubstrates; the objective lens fixed to the upper face; and the pair ofcoil substrates fixed to the pair of the side faces, wherein theobjective lens is fixed at a position displaced from a center of gravityof the lens holder to one end of the lens holder, and one of the pair ofthe coil substrates is fixed on one of the side faces of the lens holderin a range from the one end of the lens holder to a center portion ofthe lens holder, and the other one of the coil substrates is fixed onthe other one of the side faces of the lens holder in a range from theother end of the lens holder to the center portion of the lens holder.

[0010] The above actuator is used in a pickup device which is used for adrive device of an optical disc. The actuator is positioned opposing tothe optical disc to irradiates a light beam from a light source to aninformation recording surface of the optical disc. The objective lens isfixed to the lens holder forming the actuator at a position closer toone end thereof. One coil substrate is fixed on one side face of thelens holder in a range from the one end of the lens holder to a centerportion of the lens holder, and the other coil substrate is fixed on theother side face of the lens holder in a range from the other end of thelens holder to the center portion of the lens holder. Therefore, nearthe end of the lens holder on the objective lens side, the coilsubstrate is not attached to one side of the lens holder, providing aspace below the objective lens. By arranging an optical system to guidethe light beam to the objective lens via the space, the optical systemcan be arranged at the same height level as the actuator. As a result,In comparison with the case where the optical system is provided belowthe actuator, whole thickness of the pickup device can be reduced, and apreferable pickup device for a thin-type drive device may be provided.

[0011] The lens holder may have a mass portion at a side of the otherend, and the mass portion may have a mass larger than a mass of the oneend of the lens holder. By this, it is possible to correct the shift ofthe gravity center of the lens holder when the objective lens is fixednear one end thereof.

[0012] The lens holder may include a first stopper provided at the oneend and a second and a third stoppers provided at the other end, whereinthe second stopper contacts a portion of a body mounting the actuator tolimit movement of the lens holder in a focus direction of an opticaldisc, the third stopper contacts the portion of the body to limit themovement of the lens holder in a tracking direction of the optical disc,and the first stopper contacts the portion of the body to limit themovement of the lens holder in both of the focus direction and thetracking direction.

[0013] In this feature, at the end of the lens holder on the objectivelens side, one stopper can limit the strokes of the lens holder in bothfocus direction and tracking direction. Therefore, the lens holder maybe formed thinner.

[0014] The actuator may further include: an actuator base having a pairof yokes; and a pair of magnets fixed to the pair of the yokes, whereineach of the pair of the magnets may be positioned opposing to each ofthe pair of the coil substrates. In this feature, by applying a drivingcurrent to the coils on the coil substrates within the magnetic fieldcreated by the magnets, the objective lens can be moved to perform focuscontrol and tracking control.

[0015] Each of the pair of the coil substrates may include a trackingcoil and a focus coil formed in alignment with each other in ahorizontal direction of the coil substrate, and the coil substrates mayoppose to each other only in areas where the focus coil is formed. Thus,an appropriate magnetic field can be created between the coilsubstrates, and a space to arrange the optical system may be ensured.

[0016] Each of the pair of the coil substrates may include a pair oflands in an area where the focus coil is formed, and the lens holder mayfurther include connection wires which electrically connect the lands onthe pair of the coil substrates. Therefore, the coil substrates can beelectrically connected by short wires within the area in which the coilsubstrates oppose to each other.

[0017] Each of the pair of the magnets may include a magnetizationpattern having a boundary area, and an north pole area and a south polearea on both sides of the boundary area. A vertically extending portionof the boundary area may perpendicularly cross the tracking coil of thecoil substrate, and a horizontally extending portion of the boundaryarea may perpendicularly cross the focus coil of the coil substrate. Inthis feature, the tracking servo and the focus servo can beappropriately performed by the magnetic field created by the magnets andthe application of the drive current to the coils. The nature, utility,and further features of this invention will be more clearly apparentfrom the following detailed description with respect to preferredembodiment of the invention when read in conjunction with theaccompanying drawings briefly described below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIGS. 1A to 1C are diagrams showing the configuration of a pickupdevice according to the present invention;

[0019]FIGS. 2A to 2C are diagrams showing the configuration of anactuator in the pickup device of the present invention;

[0020]FIGS. 3A to 3C are diagrams showing the relative positions of coilsubstrates and magnets in the actuator;

[0021]FIGS. 4A to 4C are diagrams showing a magnetization pattern of themagnets used for the actuator of the present invention;

[0022]FIGS. 5A and 5B are diagrams showing the configuration of the coilsubstrates used for the actuator of the present invention;

[0023]FIGS. 6A and 6B are diagrams showing the relative positionalrelation between the magnets and the coil substrates;

[0024]FIGS. 7A to 7C are diagrams showing the configuration ofsuspension wires used for the actuator of the present invention;

[0025]FIGS. 8A to 8D are diagrams showing the configuration of a lensholder used for the actuator of the present invention; and

[0026]FIGS. 9A to 9C are diagrams showing stroke limitation performed bystoppers formed on the lens holder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The preferred embodiment of the present invention will now bedescribed below with reference to the attached drawings.

[0028]FIGS. 1A to 1C show the configuration of a pickup device accordingto an embodiment of the present invention. FIG. 1A is a top view of apickup device 100, FIG. 1B is a perspective view of the pickup device100, and FIG. 1C is a bottom plan view of the pickup device 100. Asshown in FIGS. 1A to 1C, the pickup device 100 has various componentsmounted on a body 1. An actuator base 8 is fixed on the body 1, and theactuator base 8 supports a lens holder 5 movably in a focusing directionF and a tracking direction T by using four suspension wires 10. The lensholder 5 has coil substrates 7 a and 7 b mounted on the opposing sidesthereof and an objective lens 4 mounted on the top surface.

[0029] Magnets 6 a and 6 b are fixed on the body 1 so as to berespectively opposed to the paired coil substrates 7 a and 7 b mountedon the lens holder 5. The paired magnets 6 a and 6 b are fixed so as tobe opposed to each other, and a magnetic field is created in a spacebetween the magnets 6 a and 6 b in accordance with the magnetizationpatterns of the magnets 6 a and 6 b. The lens holder 5 having the coilsubstrates 7 a and 7 b on the sides is placed in the magnetic fieldcreated by the paired magnets 6 a and 6 b. Thus, when a predetermineddriving current is applied to a focus coil and a tracking coil that areformed on the coil substrates 7 a and 7 b, the lens holder 5 is moved inthe focusing direction F and the tracking direction T due to forcegenerated by the currents in the coils and the magnetic field. Due tothe movement of the lens holder 5, the objective lens 4 on the lensholder 5 is moved to perform the focus control and the tracking control.

[0030] A laser light source 2 is mounted on an end of the body 1. Alaser beam emitted from the laser light source 2 passes through anoptical path 3, which is constituted by an optical system arranged inthe body 1, and reaches the position below the objective lens 4. Araise-up mirror 9 is placed below the objective lens. The raise-upmirror 9 changes the path of the laser beam upward and the laser beampasses through the objective lens 4 upwardly from below. An optical discis placed above the objective lens 4, and the objective lens 4 condensesthe laser beam on the information recording surface of the optical disc.

[0031] Next, referring to FIGS. 2A to 2C, an actuator of the pickupdevice 100 will be described below. FIG. 2A is a top view of theactuator, FIG. 2B is a perspective view of the actuator, and FIG. 2C isa bottom plan view of the actuator. The actuator 50 is a mechanism formoving the objective lens 4 in the focusing direction F and the trackingdirection T, and includes the actuator base 8, the lens holder 5, thepaired magnets 6 a and 6 b, and the paired coil substrates 7 a and 7 bmounted on the lens holder 5.

[0032] As shown in FIGS. 1A to 1C and 2A to 2C, the actuator base 8 isfixed on the body 1 of the pickup device 100. Further, a pair of yokes11 is formed on the body 1, and the magnets 6 a and 6 b are fixed insidethe yokes 11. In the pickup device 100 of the present invention, thepaired yokes 11 are not completely opposed to each other but aredisplaced from each other in the tracking direction T. This arrangementis made to provide a space for arranging an optical path (opticalsystem) 3 indicated by broken lines in FIG. 2A. The magnets 6 a and 6 bare mounted inside of the yokes 11, and hence a magnetic field iscreated in a space between the paired magnets 6 a and 6 b.

[0033] Meanwhile, on the actuator base 8, the lens holder 5 is supportedby the four suspension wires 10. The lens holder 5 is supported byelasticity of the suspension wires 10 so as to be moved in the focusingdirection F and the tracking direction T. The objective lens 4 ismounted on the lens holder 5. By applying driving current to the focuscoil and the tracking coil on the coil substrates 7 a and 7 b, which aremounted on the lens holder 5, in a magnetic field created by the pairedmagnets 6 a and 6 b, force is applied to the coil substrates 7 a and 7 bas well as the lens holder 5 integrated with the coil substrates 7 a and7 b in the focusing direction F and the tracking direction T, so thatthe objective lens 4 is moved with respect to the information recordingsurface and the information track of the optical disc.

[0034] As clearly shown in FIGS. 2A and 2B, in the pickup device 100 ofthe present invention, the paired coil substrates 7 a and 7 b arelaterally (i.e., in the tracking direction T) shifted in the oppositedirections and are not completely opposed to each other in a horizontaldirection. This arrangement is made to place the optical path 3 from thelaser light source 2 at the same height level as the magnets 6 a and 6 band the coil substrates 7 a and 7 b.

[0035] In an ordinary pickup device, paired magnets and coil substratesare almost entirely opposed to each other in the width direction. Thus,the magnets and the coil substrates cover both sides of an objectivelens like walls and a laser beam cannot be directed to the objectivelens at the same height level. Hence, the optical path of the laser beamhas to be placed at a lower height than the magnets and the coilsubstrates, thereby increasing the entire thickness of the pickupdevice.

[0036] On the contrary, in the actuator 50 of the present invention, themagnets 6 a and 6 b and the coil substrates 7 a and 7 b are displacedfrom each other oppositely in the tracking direction T. Namely, thepaired magnets 6 a and 6 b are only partially opposed to each other, andthe coil substrates 7 a and 7 b are only partially opposed to eachother. Thus, as shown in FIGS. 2A and 2B, the objective lens 4 partiallyforms a space in the circumferential direction. The optical path 3 isplaced in the space and a laser beam from the laser light source 2 isintroduced to a position below the objective lens 4. With thisconfiguration, it is possible to arrange the magnets 6 a and 6 b, thecoil substrates 7 a and 7 b, and the optical path 3 of a laser beam fromthe laser light source 2 at the same height level, thereby reducing theentire height (thickness) of the pickup device.

[0037]FIGS. 3A to 3C show the positional relation between the magnetsand the coil substrates. FIG. 3A shows the arrangement of the magnets 6a and 6 b with respect to the actuator 50, FIG. 3B shows the arrangementof the coil substrates 7 a and 7 b with respect to the actuator 50, andFIG. 3C shows the arrangement of the magnets 6 a and 6 b and the coilsubstrates 7 a and 7 b with respect to the actuator 50. Besides, FIGS.3A to 3C show that the magnets and the coil substrates are removedupward from the mounting positions. Namely, in FIGS. 3A to 3C, themagnets and the coil substrates are moved from the illustrated positionsin parallel to lower positions and are fixed thereon.

[0038] As shown in FIG. 3A, the magnets 6 a and 6 b are fixed inside theyokes 11 so as to be opposed to each other. Moreover, as shown in FIG.3B, the coil substrates 7 a and 7 b are respectively mounted on thesides along the longitudinal direction of the lens holder 5. As alreadymentioned, the lens holder 5 is movably supported by the four suspensionwires 10 in the space between the magnets 6 a and 6 b. As a result, asshown in FIG. 3C, the magnet 6 a and the coil substrate 7 a arepositioned close to each other, and the magnet 6 b and the coilsubstrate 7 b are positioned close to each other.

[0039]FIGS. 4A to 4C are plan views showing the magnets. FIG. 4A showsthe magnet 6 a, and FIG. 4B shows the magnet 6 b. The magnets 6 a and 6b are produced by magnetizing iron pieces of a predetermined size byusing a magnetizing device. With the magnetizing device, illustratedmagnetization patterns are formed on the magnets 6 a and 6 b. As shownin FIG. 4A, the magnet 6 a has the magnetization pattern constituted bya magnetized area 18 a of north pole, a magnetized area 19 a of southpole, and a boundary area 20 a between the areas 18 a and 19 a. Further,as shown in FIG. 4B, the magnet 6 b has the magnetization patternconstituted by a magnetized area 18 b of north pole, a magnetized area19 b of south pole, and a boundary area 20 b between the areas 18 b and19 b.

[0040]FIG. 4C shows the positional relation between the magnets 6 a and6 b. As shown in FIG. 3A, the magnets 6 a and 6 b are fixed respectivelyon the yokes 11 so as to be opposed to each other. FIG. 4C shows thepositional relation between the magnetization patterns of the magnets 6a and 6 b in a state in which the magnets 6 a and 6 b are opposed toeach other on the yokes 11. FIG. 4C shows the relative positionalrelation between the magnetization patterns of the magnets 6 a and 6 b,taken from the direction of an arrow 80 in FIG. 3A. The magnet 6 a isindicated by broken lines and the magnet 6 b is indicated by solidlines.

[0041] As shown in FIG. 4C, the magnets 6 a and 6 b are partiallyopposed to each other and partially has an overlap in the lateraldirection when viewed from the direction of the arrow 80. At this point,in the perspective view taken from the direction of the arrow 80 in FIG.3A, the north pole magnetized area 18 a of the magnet 6 a and the northpole magnetized area 18 b of the magnet 6 b overlap with each other, andthe south pole magnetized area 19 a of the magnet 6 a and the south polemagnetized area 19 b of the magnet 6 b overlap with each other. Inaddition, the boundary area 20 a of the magnet 6 a and the boundary area20 b of the magnet 6 b overlap with each other. As a result, asubstantially recessed magnetic field, which corresponds to themagnetization pattern (hereinafter referred to as a “combinedmagnetization pattern”) schematically shown in FIG. 4C, is formed in aspace between the magnets 6 a and 6 b, that is, a space in which thelens holder 5 is placed.

[0042] Next, the coil substrates will be described. FIG. 5A is a planview of the coil substrate 7 a, and FIG. 5B is a plan view of the coilsubstrate 7 b. The coil substrate 7 a is a printed wiring board and hasa tracking coil 13 a and a focus coil 14 a formed on the substratesurface. Further, lands 15 a and 16 a are formed on the coil substrate 7a to establish continuity with the opposed coil substrate 7 b.

[0043] Meanwhile, the coil substrate 7 b is also a printed wiring boardand has a tracking coil 13 b and a focus coil 14 b formed on thesubstrate surface. Moreover, lands 15 b and 16 b are formed on the coilsubstrate 7 b to establish continuity with the opposed coil substrate 7a. In the state being mounted on the sides of the lens holder 5, thefocus coil 14 a of the coil substrate 7 a and the focus coil 14 b of thecoil substrate 7 b are substantially opposed to each other.

[0044]FIG. 6A shows the relative positional relation between the coilsubstrates 7 a and 7 b in a state being mounted on the lens holder 5.FIG. 6A perspectively shows the relative positional relation between thecoil substrates 7 a and 7 b on the lens holder 5, viewed in thedirection of the arrow 81 in FIG. 3B. The coil substrate 7 a isindicated by broken lines and the coil substrate 7 b is indicated bysolid lines. As shown in FIG. 6A, the coil substrates 7 a and 7 b aremounted on the lens holder 5 with a such relative positional relationthat the focus coils 14 a and 14 b are substantially overlap with eachother, when viewed from the side of the lens holder 5. Further, in thatstate, the land 15 a of the coil substrate 7 a and the land 15 b of thecoil substrate 7 b are opposed to each other, and the land 16 a of thecoil substrate 7 a and the land 16 b of the coil substrate 7 b areopposed to each other. In a state in which the coil substrates 7 a and 7b are mounted on the lens holder in this manner, the opposed land 15 aand 15 b and the opposed land 16 a and 16 b are electrically connectedvia connecting wires 22 (see. FIGS. 3A to 3C). This electric connectionapplies driving current to the tracking coil 13 b and the focus coil 14b of the coil substrate 7 b.

[0045]FIG. 6B shows a magnetic field created by the magnets 6 a and 6 band the arrangement of the tracking coil and the focus coil in themagnetic field. As shown, the magnets 6 a and 6 b create a magneticfield corresponding to the combined magnetization pattern of asubstantially recessed shape (indicated by broken lines) in FIG. 6B. Theboundary area 20 a of the magnet 6 a shown in FIG. 4A longitudinallypenetrates nearly the center of the rectangular tracking coil 13 a ofthe coil substrate 7 a shown in FIG. 5A. The boundary area 20 b of themagnet 6 b shown in FIG. 4B penetrates nearly the center of therectangular tracking coil 13 b of the coil substrate 7 b shown in FIG.5B. Further, the boundary areas 20 a and 20 b of the magnets 6 a and 6 blaterally penetrate nearly the center of the rectangular focus coils 14a and 14 b of the coil substrates 7 a and 7 b. The lens holder 5 onwhich the coil substrates 7 a and 7 b are attached is placed in thespace between the magnets 6 a and 6 b so as to establish such relativepositional relations.

[0046] Next, the arrangement of the suspension wires 10 will bedescribed. The suspension wire 10 is made from a linear metal havingelasticity, and so on. In the actuator 50 of the present invention, thelens holder 5 is supported by the four suspension wires 10. As shown inFIGS. 1A and 3A, the ends of the four suspension wires 10 are fixed onthe actuator base 8 and the other ends are fixed on the coil substrates7 a and 7 b integrated with the lens holder 5. Thus, the lens holder 5is placed in the space between the magnets 6 a and 6 b while beingsupported by the four suspension wires 10 in the horizontal direction.By the elasticity of the suspension wires 10, the lens holder 5 holdingthe objective lens 4 can move in the focusing direction F and thetracking direction T that are perpendicular to the longitudinaldirection (jittering direction J) of the suspension wires 10.

[0047]FIG. 7A shows the relative positional relationship between theactuator base 8, the suspension wires 10 and the lens holder 5. In thepresent invention, in order to place the optical path of the laser beamat the same vertical level as the coil substrate 7, the two opposed coilsubstrates 7 a and 7 b are mounted on the lens holder 5 with beingshifted in the lateral direction (tracking direction T). Therefore, thesuspension wires 10 are not in parallel with the jittering direction J.Namely, the suspension wires 10 are extended in a direction having apredetermined angle from the jittering direction J, and the ends of thesuspension wires 10 are fixed on the actuator base 8.

[0048] Referring to FIGS. 7B and 7C, the above configuration will bedescribed in detail. FIG. 7B shows the relative positional relationbetween a typical actuator base, suspension wires and a lens holder. InFIG. 7B, a lens holder 121 is supported by four suspension wires 124from an actuator base 123. It is to be noted that, since FIG. 7B is aplan view showing the top of the actuator, only the two upper suspensionwires are shown. An objective lens 120 and a pair of coil substrates 122a and 122 b are mounted on the lens holder 121. As shown in FIG. 7B,when the paired coil substrates 122 a and 122 b are placed on both sidesof the lens holder 121 so as to be completely opposed to each other(namely, without the shift in the tracking direction T, unlike thepresent invention), the four suspension wires 10 fixed on the actuatorbase 8 and the lens holder 121 are arranged in parallel with each other.

[0049] On the other hand, FIG. 7C schematically shows the relativepositional relation between the actuator base 8, the suspension wires 10and the lens holder 5 in the actuator 50 of the present invention. Inthe case of the present invention, the coil substrates 7 a and 7 b aremounted on the sides of the lens holder 5 so as to be partially opposedto each other. Specifically, the coil substrate 7 a is shifted downwardin FIG. 7C and the coil substrate 7 b is shifted upward in FIG. 7C tocreate the space for arranging the optical path 3.

[0050] Therefore, the suspension wires 10 are not in parallel with eachother, but are somewhat opened to the direction of the lens holder 5.Specifically, as shown in FIG. 7C, each of the suspension wires 10 isextended to the lens holder 5 at an angle increased by an angle a fromthe direction of the lens holder 5 (that is, the jittering direction J),and the ends of the suspension wires 10 are fixed on the actuator base8. Moreover, as is evident from comparison with FIG. 7B, the fixingpositions 31 and 32 of the suspension wires 10 to the actuator base 8are shifted by a distance L in the jittering direction J. Namely, a lineconnecting the fixing positions 31 and 32 of the suspension wires to theactuator base 8 is not arranged in parallel with the coil substrates 7 aand 7 b. The reason is as follows. Since the supporting positions of thesuspension wires 10 on the side of the lens holder 5 are arranged atdifferent levels with respect to the jittering direction J, when thesupporting positions of the suspension wires 10 on the side of theactuator base 8 are not shifted in the jittering direction J, the foursuspension wires 10 cannot have equal length, thereby breaking therelation between the center of gravity of the lens holder 5 and thespring constants of the four suspension wires 10. In order to preventthis problem, the supporting positions 31 and 32 of the suspension wires10 on the side of the actuator base 8 are shifted in the jitteringdirection J and the four suspension wires are made equal in length.

[0051] Moreover, when suspension wires of equal lengths are used, thenumber of components can be reduced, thereby reducing the product cost.However, it is not always necessary to have suspension wires of equallengths and various lengths are applicable. In that case, theconfiguration can be made by suitably setting spring constants and thelike of the suspension wires.

[0052] Further, FIG. 7C only shows the two upper suspension wires 10 ofthe four suspension wires 10 in the focusing direction. The two lowersuspension wires 10 are held below and in parallel with the two uppersuspension wires 10.

[0053] In this way, in the actuator 50 of the present invention, thedirections of the suspension wires 10 are not arranged in parallel butare somewhat opened to the lens holder 5. One of the reasons is that,since the width of the lens holder is increased in the trackingdirection by shifting the position of the coil substrates, a springinterval (i.e., the interval between the supporting wires 10) on theside of the actuator is reduced to have a smaller projection area overthe pickup. Another reason is that, by providing suspension wires notbeing in parallel, the spring constant of the suspension wires isincreased in a twisting direction viewed from the arrow 81 of FIG. 3, sothat a mode frequency (rolling frequency) in the twisting direction canbe higher than a parallel spring. Further, the fixing positions 31 and32 of the suspension wires 10 on the side of the actuator base 8 areshifted in the jittering direction J.

[0054] Next, the lens holder will be described below. FIGS. 8A to 8Dshow the configuration of the lens holder 5. FIG. 8A is a top view ofthe lens holder 5, FIG. 8B is a bottom plan view of the lens holder 5,FIG. 8C is a perspective view of the lens holder 5 obliquely viewed fromabove, and FIG. 8D is a perspective view of the lens holder 5 obliquelyviewed from below.

[0055] As shown in FIGS. BA to 8D, the lens holder 5 has a mounting hole40 for mounting the objective lens 4. The mounting hole 40 is shiftedfrom a gravity center 41 of the lens holder 5 to the side of the opticalpath 3. The objective lens is normally placed around the center of thelens holder (around the center of gravity of the lens holder, see FIG.7B). However, in the present invention, the pickup 100 is configured sothat the coil substrates 7 a and 7 b mounted on the lens holder 5 areshifted in the tracking direction T to obtain the optical path fordirecting a laser beam to below the objective lens. Thus, the positionmounting the objective lens on the lens holder 5 is shifted to theoptical path 3 of the laser beam. Since the optical path 3 of a laserbeam has to reach below the objective lens 4, when the objective lens 4is positioned around the center of the lens holder 5, the optical path 3of the laser beam has to reach around center of the lens holder 5.Accordingly, the coil substrate 7 b on the side of the optical path 3should be shifted more largely to obtain a larger space on the side ofthe lens holder 5. On the contrary, as shown in FIG. 8A, when theposition of the objective lens 4 (that is, the position of the mountinghole 40) is shifted to the optical path 3, the optical path 3 is placedcloser to the end of the lens holder 5, thereby reducing a shiftingamount of the coil substrate 7 b on the side of the optical path 3.Hence, it is possible to reduce the length of the lens holder 5.

[0056] Moreover, when the mounting position of the objective lens 4 onthe lens holder 5 is shifted in the direction of the optical path 3, thecenter of gravity of the lens holder 5 itself is shifted to the opticalpath 3 side after mounting the objective lens 4. Therefore, as shown inFIGS. 8C and 8D, the configuration of the lens holder 5 is devised asfollows. Namely, the wall parts 42 and 43 on the opposite side of theobjective lens 40 of the lens holder 5 are formed with a largerthickness than a part 44 on the side of the objective lens mounting hole40, for example, and the center of gravity of the lens holder 5 ispositioned substantially at the center when the objective lens 4 ismounted on the lens holder 5. In this way, the shift of the center ofgravity of the lens holder, that may happen by shifting the position ofthe objective lens in the direction of the optical path, is cancelled.

[0057] Further, as shown in FIG. 8A, the fixing positions 33 and 34 ofthe suspension wires 10 to the lens holder 5 have a midpointsubstantially coinciding with the gravity center 41 of the lens holder 5supported by the suspension wires 10. Namely, in FIG. 8A, the suspensionwires 10 are each fixed on the lens holder 5 (to be precise, the coilsubstrates 7 b and 7 a mounted on the lens holder 5) at the fixingpositions 33 and 34. In this case, the midpoint of the fixing positions33 and 34 substantially coincide with the gravity center 41 of the lensholder 5. As a result, both ends of the lens holder 5 can be held by thesuspension wires 10 with being equally balanced, thereby preventingrolling and the like of the lens holder 5.

[0058] Further, as shown in FIGS. 8A to 8D, the lens holder 5 includesstoppers 59, 51 and 52. The stoppers 59, 51 and 52 play a role oflimiting the stroke (movable range) of the lens holder 5 in the focusingdirection F and the tracking direction T. Thus, when a focus servo or atracking servo causes a malfunction, it is possible to prevent the lensholder 5 from moving unlimitedly, making contact with the body 1 and theother members, and damaging the lens holder 5, the objective lens 4 andso on.

[0059] In the lens holder 5 of the present invention, the stopper 59 hasboth functions of a stopper in the focusing direction F and a stopper inthe tracking direction T. Namely, the movement of the lens holder 5 inthe focusing direction F is limited by the stoppers 59 and 51, and themovement of the lens holder 5 in the tracking direction T is limited bythe stoppers 59 and 52.

[0060]FIG. 9A shows a state in which the stroke is limited in thefocusing direction F by the stoppers 59 and 51. The stopper 59(indicated by broken lines) makes contact with a cover 55 of the body 1from below and the stopper 51 similarly makes contact with a cover 56 ofthe body 1 from below, thereby limiting the movement of the lens holder5 in the focusing direction F (i.e., the upward direction in FIG. 9A).

[0061]FIGS. 9B and 9C show that the stroke is limited in the trackingdirection T by the stoppers 59 and 52. In FIG. 9B, the stopper 59 makescontact with the side wall of a recessed part 57 provided on the body 1.In FIG. 9C, the stopper 52 makes contact with the side wall of arecessed part 58 provided on the body 1. Thus, the moving range of thelens holder 5 is limited in the tracking direction T.

[0062] As described above, in the lens holder 5 of the presentinvention, the position of the objective lens 4 is shifted in thedirection of the optical path 3. In addition, as well shown in FIG. 8D,the portion of the lens holder 5 on the side of the mounting hole 40 ofthe objective lens has a relatively small thickness and the portion ofthe lens holder 5 on the opposite side to the mounting hole 40 has arelatively large thickness to adjust the center of gravity of the lensholder 5. Moreover, it is desirable to minimize the number of membersprovided in the direction of the optical path 3 around the mounting hole40 so as not to interrupt the optical path of a laser beam reachingbelow the objective lens 4 from the laser light source 2. For thesereasons, the stopper 59 has stroke limiting functions both in thefocusing direction F and the tracking direction T.

[0063] As described above, according to the actuator of the presentinvention, the pair of coil substrates mounted on the lens holder isshifted in the longitudinal direction (tracking direction T) of the lensholder to obtain the optical path for directing a laser beam to theposition below the objective lens. Thus, it is possible to direct alaser beam to the position below the objective lens at the same heightlevel as the coil substrates and the magnets, thereby reducing thethickness of the whole actuator.

[0064] The invention may be embodied on other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresent embodiments therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning an range ofequivalency of the claims are therefore intended to embraced therein.

[0065] The entire disclosure of Japanese Patent Application No.2002-152061 filed on May 27, 2002 including the specification, claims,drawings and summary is incorporated herein by reference in itsentirety.

What is claimed is:
 1. An actuator comprising: a lens holder having anupper face for holding an objective lens and a pair of side faces forholding coil substrates; the objective lens fixed to the upper face; andthe pair of coil substrates fixed to the pair of the side faces, whereinthe objective lens is fixed at a position displaced from a center ofgravity of the lens holder to one end of the lens holder, and one of thepair of the coil substrates is fixed on one of the side faces of thelens holder in a range from the one end of the lens holder to a centerportion of the lens holder, and the other one of the coil substrates isfixed on the other one of the side faces of the lens holder in a rangefrom the other end of the lens holder to the center portion of the lensholder.
 2. The actuator according to claim 1, wherein the lens holderhas a mass portion at a side of the other end, the mass portion having amass larger than a mass of the one end of the lens holder.
 3. Theactuator according to claim 1, wherein the lens holder comprises a firststopper provided at the one end and a second and a third stoppersprovided at the other end, the second stopper contacts a portion of abody mounting the actuator to limit movement of the lens holder in afocus direction of an optical disc, the third stopper contacts theportion of the body to limit the movement of the lens holder in atracking direction of the optical disc, and the first stopper contactsthe portion of the body to limit the movement of the lens holder in bothof the focus direction and the tracking direction.
 4. The actuatoraccording to claim 1, further comprising: an actuator base having a pairof yokes; and a pair of magnets fixed to the pair of the yokes, whereineach of the pair of the magnets is positioned opposing to each of thepair of the coil substrates.
 5. The actuator according to claim 4,wherein each of the pair of the coil substrates comprises a trackingcoil and a focus coil formed in alignment with each other in ahorizontal direction of the coil substrate, and the coil substratesoppose to each other only in areas where the focus coil is formed. 6.The actuator according to claim 5, wherein each of the pair of the coilsubstrates comprises a pair of lands in an area where the focus coil isformed, and the lens holder further comprises connection wires whichelectrically connect the lands on the pair of the coil substrates. 7.The actuator according to claim 4, wherein each of the pair of themagnets comprises a magnetization pattern having a boundary area, and annorth pole area and a south pole area on both sides of the boundaryarea, a vertically extending portion of the boundary areaperpendicularly crosses the tracking coil of the coil substrate, and ahorizontally extending portion of the boundary area perpendicularlycrosses the focus coil of the coil substrate.